1. Field of the Invention
The present invention relates generally to a clutch actuator, more particularly to an ergonomic manual clutch actuator assembly for a motorcycle for reducing operator fatigue.
2. Background Art
Straddle-type vehicles, particularly motorcycles, include a motor for imparting power to a transmission for driving the vehicle. Typically, the motor is an internal combustion engine and the transmission has a plurality of gear reduction ratios for offering a variety of operable modes to a user. In order to shift between gear reduction ratios of the transmission, a clutch is typically utilized between the motor or engine and the transmission. The clutch may be actuated by an actuator that may receive a signal from the user or from an engine control unit, signaling to engage or disengage the clutch.
Alternatively, and more commonly, the clutch is actuated by a manually imparted force through a manual clutch lever, which is pivotally mounted to a handlebar of the motorcycle adjacent to a hand grip on the handlebar. Due to varying demographics within the market of straddle-type vehicle consumers, it is desired to allow the user to manually operate the clutch to provide the user with enjoyment of controlling the operation of the vehicle. This clutch operation typically requires that the user grip the clutch lever and actuate it to a retracted position, relatively close to the handlebar grip, to thereby actuate the clutch to a disengaged position. After a desired gear reduction ratio is selected of the transmission, the user releases its grip upon the manual clutch lever and the clutch reengages.
Conventional clutches, particularly on straddle-type vehicles such as motorcycles, include a friction type clutch that is normally biased to the engaged mode by a clutch spring. The operation of the manual clutch lever draws a clutch cable which is connected to a clutch shaft and the drawn clutch cable actuates the clutch shaft to a disengaged position of the clutch. Accordingly, when the user releases its grip, the clutch spring biases the clutch shaft back to the engaged position of the clutch.
The prior art teaches various clutch actuators for actuating the clutch shaft to the disengaged position upon being drawn by the clutch cable. For example, in straddle-type vehicles that have a high torque output, a correspondingly high force of friction is required to maintain the engagement of a clutch. This high force of friction is generated through mating clutch plates having a high coefficient of friction and large contact area, and a relatively heavy duty clutch spring that has a relatively high spring coefficient for imparting the necessary load. Accordingly, a large manual force is required to actuate the clutch shaft. The force required to displace the clutch shaft increases with the increasing displacement of the clutch shaft due to the increasing relative compression or extension of the clutch spring. Accordingly, in order to maintain the clutch in a disengaged position, a generally increasing force is required having a peak at the disengaged position. In other words, if the user desires to keep the clutch disengaged, the user must maintain the clutch lever in the retracted position corresponding with the highest requirement of manually imparted force.
It is desirable among straddle-type vehicle consumers, particularly motorcycle users, to keep the clutch disengaged when temporarily stopped during use. For example, if a motorcyclist stops at a stop sign or a stop light, the user prefers to keep the clutch disengaged so that the user may shift the motorcycle to the appropriate gear. The alternative of leaving the clutch engaged at a stop would require shifting the transmission into neutral. The preferred method of keeping the clutch disengaged and the transmission in the appropriate gear allows the user to enjoy a quick start or acceleration from the stop position. This option offers benefits both in safety and in user enjoyment. The drawback to this option, however, is the user must maintain the clutch lever in the fully retracted position, which also corresponds with the maximum manual imparted force. As time and repetitions increase, the hand of the operator experiences fatigue which may be undesirable.
Referring again to straddle-type vehicles having a high torque output, a relatively heavy duty actuator is required to actuate the clutch shaft. One such prior art design includes a swash plate which engages the clutch shaft. The swash plate includes an array of rollers secured thereto for riding within a corresponding array of arcuate, tapered tracks. The swash plate is coupled to the clutch cable so that as the clutch cable is drawn, the swash plate rotates and the rollers riding within the tapered tracks rise, thus axially displacing the swash plate and actuating the clutch shaft. The clutch cable is typically pivotally connected to the swash plate at a radial position thereof. Therefore, as the clutch cable is drawn, it rotates the swash plate, yet also applies a load to the swash plate in a direction of the clutch cable. This load increases friction between the swash plate and rollers, and between the rollers within the corresponding tapered tracks. This friction reduces the efficiency of the clutch actuator and adds to the manually imparted force required to actuate the clutch.
Cable drawn clutch actuators typically include a cable sheathing for covering the length of the cable, thus protecting the cable from elements and the like, and for securing distal ends of the cable to thereby provide fixed locations of the cable. However, the sheathing also generates friction as the clutch cable is drawn and released.
In summary, a user must overcome cable friction, friction associated with the clutch actuator, loads associated with clutch spring displacement and inefficiencies incorporated within the overall assembly.
In the modern age of straddle-type vehicle marketing, there is a range of consumer products including both modernistic styling and design, and traditional styling and design. Therefore, improvements or changes to operational equipment of a straddle-type vehicle may be more desirable if inconspicuous.
What is needed is a compact, efficient, non-apparent, low-cost, ergonomic manual clutch actuator assembly for a motorcycle, wherein the manual imparted force to the clutch lever in the retracted position is less than the manual force required in an intermediate position of the clutch lever, thereby reducing operator fatigue; and a method for providing the same.